1. Field of the Invention
The present invention relates to an apparatus for mixing viscous material.
2. Description of the Related Art
In a viscous material mixing device for mixing high-viscosity polymer material with a viscosity over a certain level to induce reaction for the purpose of obtaining a desired polymer product, one of the important factors is effective heat exchange, namely rapidly discharging the heat, generated during the reaction, out of the mixing device or effectively supplying heat required for the reaction. The heat exchange includes cooling or heating polymer material by applying coolant or heating agent to the mixing device.
For performing the heat exchange, a chamber in which polymer material is stirred should be cooled. However, if the polymer material is adhered to the wall of the chamber due to their viscosity, the heat of coolant or heating agent is not easily transferred into the chamber. In severe cases, it may be impossible to produce a polymer product including a heat-sensitive reaction process.
FIG. 1 shows an example of a conventional viscous material mixing device 11.
As shown in FIG. 1, the conventional mixing device 11 includes a chamber 13 for receiving high-viscosity material Z to be mixed, a draft tube 19 fixed in the chamber 13, and a carrying impeller 30 rotatably installed in the draft tube 19 and driven using the power transmitted from an external motor 31.
The chamber 13 includes a bottom 13a, a cylindrical sidewall 13b fixed to the bottom to form an inner space 13c of a predetermined capacity, and a cover 14 for covering the upper portion of the sidewall 13b. In particular, a heat medium passage 15 is provided in the sidewall 13b. The heat medium passage 15 is connected to a heat medium supply pipe 17a and a heat medium discharge pipe 17b, and it receives a heat medium supplied through the heat medium supply pipe 17a, flows the heat medium therein and then discharge the heat medium through the heat medium discharge pipe 17b. The heat medium passes through the heat medium passage 15 and it is used for heat exchange with the high-viscosity material Z.
The draft tube 19 is a cylindrical member with a constant diameter, and its upper and lower ends are open. The draft tube 19 is spaced apart from the bottom 13a by means of a plurality of legs 20. In addition, a heat medium passage 21 is also provided in a sidewall 19a of the draft tube 19. The heat medium passage 21 is connected to a heat medium supply pipe 23a and a heat medium discharge pipe 23b, and it allows the heat medium supplied through the heat medium supply pipe 23a to flow therein and then discharges the heat medium through the heat medium discharge pipe 23b. The heat medium passing through the heat medium passage 21 is also used for heat exchange with the high-viscosity material Z.
Meanwhile, the carrying impeller 30 installed in the draft tube 19 includes a driving shaft 27 vertically extended and axially rotated with a torque transmitted from the motor 31, and a blade 29 fixed to the outer circumference of the driving shaft 27 and spirally extended thereon. In particular, the outer front end of the blade 29 is as closer to the inner circumference of the draft tube 19 as possible.
A flow guider 25 is provided below the carrying impeller 30. The flow guider 25 has a conical shape inclined downward in a radial direction, and the flow guider 25 guides the high-viscosity material Z, moving downward through the carrying impeller 30, to a space 33 between the draft tube 19 and the chamber 13.
Reference numeral 28 designates a bearing. The bearing 28 is positioned at the center of the cover 14 and the flow guider 25 and supports the driving shaft 27 vertically.
If the carrying impeller 30 of the mixing device 11 configured as mentioned above is driven, the high-viscosity material Z in the draft tube 19 moves down along the arrowed direction out of the draft tube 19, and then the high-viscosity material Z is guided in a radial direction by the flow guider 25 and moves upward via the space 33.
The space 33 is an empty space between the draft tube 19 and the sidewall 13b, acting as a passage for the high-viscosity material Z to move upward. The high-viscosity material Z passing through the space 33 upward is sucked into the draft tube 19 due to the action of the carrying impeller 30. As a result, the high-viscosity material Z is mixed with circulating a path of moving downward out of the draft tube 19 and flowing upward through the space 33, and then returning to the draft tube 19.
While the high-viscosity material Z is circulated, the heat medium continuously passes through the heat medium passages 15, 21. The heat medium is used for cooling or heating the high-viscosity material Z, and the heat possessed by the heat medium is transferred to the high-viscosity material Z through the thickness of the sidewalls 19a, 13b. 
In particular, the high-viscosity material Z is pressed in an arrow C direction and pushed outward by the rotating blade 29. At this time, due to the cohesion of the high-viscosity material itself and the kinetic energy applied by the blade 29 in the arrow C direction, the high-viscosity material positioned near the front end of the blade 29 is cut to form a space E.
The space E is a portion to which the high-viscosity material is not adhered, and it may allow the heat to rapidly pass through the sidewall 19a in its thickness direction, not being disturbed by the high-viscosity material. That is to say, the space E allows the heat, transferred from outside, to reach more deeply into the draft tube 19 due to the convection, thereby improving the heat exchange efficiency. An arrow A designates a flow of hot or cold air supplied from the heat exchange medium.
However, the conventional mixing device 11 shows low heat exchange efficiency in areas except the inner circumference of the draft tube 19 (e.g., the outer circumference of the draft tube or the inner circumference of the sidewall).
If the high-viscosity material Z is not adhered to the heat exchange path, the supplied heat may pass through only the sidewalls 13b, 19a and be transferred more deeply into the high-viscosity material Z. However, since the high-viscosity material is adhered to the outer circumference of the draft tube and the inner circumference of the sidewall, the adhered layer disturbs heat transfer (though the adhered layer allows heat exchange to some extent), and thus the heat cannot reach the inside of the high-viscosity material.
FIG. 2 is for illustrating flow characteristics in an A portion of the mixing device of FIG. 1.
As shown in FIG. 2, as for the high-viscosity material Z passing through the space 33 upward, it would be understood that high-viscosity material located near the sidewalls 13b, 19a is nearly not flowing since its flowing rate is very low in comparison to the main stream at the center. It is due to the viscosity possessed by the high-viscosity material.
The high-viscosity material stagnated near the sidewalls 13b, 19a is positioned as one adhered layer, which disturbs the heat supplied from the heat medium not to be transferred into the space 33. That is to say, the adhered layer reduces the heat exchange efficiency in the mixing device.
As mentioned above, the conventional mixing device has very low heat exchange efficiency since high-viscosity material to be mixed is adhered to the inner wall of the chamber or the draft tube, and accordingly the conventional mixing device cannot be applied to treating material that should be mixed only below a certain temperature.